There have been times in my life when I've worked out like a maniac. Hit up the gym every day with one of my besties the summer after my senior year of high school ... slavishly devoted myself to Jillian Michaels DVDs day in and day out as recently as the last year or two. But every time I've put myself through periods of rigorous, regular workouts, a.) the scale wouldn't really budge and b.) I would end up totally run down and feeling like crap. I had a pretty valid case for throwing in the towel again and again. Nonetheless, I managed to lose 40 pounds my freshman year of college almost exclusively by changing my eating habits.

Sure, there are a SLEW of reasons why working out doesn't translate on the scale. "Muscle weighs more than fat!" "Exercise makes you want to eat more!" "You work out, but then think you can get away with eating more, so calories in-calories out cancels out!"

But I only recently learned what was actually standing in my way ...

STRESS!

See, a recent saliva test showed I run low on cortisol, the stress "fight-or-flight" hormone that's needed for tons of body functions -- from regulating blood sugar to kidney function, muscle building and immune function. You need cortisol to cope with stress; that's why when you're shocked -- like, you almost get into a car accident, say -- your adrenal glands push out more of it. My adrenal glands already don't produce enough, so when I push myself too hard in my workouts, my adrenals try so hard to keep up, to produce more cortisol, but they can't, and I end up suffering adrenal fatigue. Of course, this all plays into why intense cardio equals a stubborn scale and feeling like someone ran me over with a truck.

Similarly, a lot of women run high on cortisol, because they're chronically stressed. And more cortisol equals excess glucose which gets stored as fat. Lose-lose, right?

So, finally science is confirming what we as women already know: We need stress-management and adequate sleep to lose weight. This week, a study from Kaiser Permanente found that people who slept too little or too much and reported high levels of stress were only half as likely to make it to the second phase of the study as those who got 6-8 hours of sleep and had low stress.

Also, weight loss was linked to reductions in stress and depression over time, so obviously, people who want to shed pounds have to focus on proper sleep and minimizing stress.

These researchers explain it by saying that when you're stressed you might reach for more junk food, which can contribute to extra poundage. But I know there's more to it than that. Stress and out-of-whack hormones truly hold your ability to lose weight hostage.

Personally, I've come to the conclusion that a slavish devotion to intense cardio however many times a week just isn't suitable for me. Plain and simple, it's not doing my body's rhythm any favors. I'll have to burn excess calories with less abrasive workouts, like brisk walks and yoga. There's no shame in that. And obviously managing my stress is key. It's definitely harder than it sounds, but it's gonna be so worth it.